This invention relates to method and apparatus for spray drying liquids such as slurries and the like. The basic combination of a spray drying chamber through which a generally cyclonic flow of heated drying gas is maintained, and with there being a spray-producing rotatable head disposed in such chamber which discharges the liquid to be spray dried in finally divided form in directions essentially transverse to the cyclonic flow of heated gas are old and well known. Many efforts have been made to enhance the spray-producing action so as to assure extremely divided form of the liquid as it is discharged centrifugally from the rapidly rotating spray-producing head, thereby to maximize the surface-to-volume ratio of the droplets produced correspondingly to maximize the drying action within the chamber.
Whereas the prior art systems obtain satisfactory drying, they do not make optimum use of the hot air or gas to vaporize the moisture of the slurry by transferring the sensible heat during the period of dispersion and discharge of the liquid by the spray-producing head. Moreover, the prior art devices often are characterized by the fact that the finest particles of liquid become trapped in the more or less stagnant center of the hot gas flow. This leads to inefficiency because the smallest particles are of course most propense to rapid drying and therefore should not remain in the more or less stagnant center of the air flow but should be moved outwardly so as to achieve the most efficient and effective drying action.